<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .parent {
            width: 400px;
            height: 400px;
            background: red;
        }

        .first {
            width: 100px;
            height: 100px;
            background: green;
            margin-bottom: 100px;
        }

        .second {
            margin-top: 100px;
            width: 100px;
            height: 100px;
            background: yellow;
        }
    </style>
</head>

<body>
    <div class="parent">
        <div class="first"></div>
        <div class="second"></div>
    </div>
</body>

</html>